A good charger will charge the battery at the appropriate rate so as not to produce any hydrogen.

Which is why adding a car battery to a UPS is wrong. The charger isn't designed to charge a car battery.

A SLA battery requires a lower charge rate than a car battery, which is why putting a car battery on a UPS isn't an issue.
A really cheap UPS may have problems because the time to fully charge a large capacity battery is that much longer. But it's the cheap UPS that might have problems, not the battery. Many car batteries these days are maintenance free- ie sealed. Just like the smaller capacity batteries used in UPSs.Grant
Darwin NT

I've read that telephone offices used to be required to have a UPS that could keep everything essential in that office running for three days. You might ask telephone offices if they have one they can donate. Warning - expect it to fill an entire room; I've seen one. It had a large rack of 2 volt cells, made with lead and something other than the usual acid.

The UPS for each of my desktops has a connection to that desktop that allows it to tell that desktop that it is running low on power, and that desktop should use the rest for going into sleep mode (suspending nearly all programs, then writing the contents of the entire memory to a hard drive, then adjusting the boot procedure to reload memory from that hard drive file instead of a normal boot, then turning off the power). Are your servers capable of that? The software I've seen for this is for Windows only.

I've read that telephone offices used to be required to have a UPS that could keep everything essential in that office running for three days. You might ask telephone offices if they have one they can donate. Warning - expect it to fill an entire room; I've seen one. It had a large rack of 2 volt cells, made with lead and something other than the usual acid.

I kinda think they might just be a bit too large!:-) Also they supplied 50V

That is an accurate picture of a UK telephone exchange battery room as I used to work in telephone exchanges. I think that most nowadays have diesel generators "Sometimes it is the people no one imagines anything of who do the things that no one can imagine."

The UPS for each of my desktops has a connection to that desktop that allows it to tell that desktop that it is running low on power, and that desktop should use the rest for going into sleep mode (suspending nearly all programs, then writing the contents of the entire memory to a hard drive, then adjusting the boot procedure to reload memory from that hard drive file instead of a normal boot, then turning off the power). Are your servers capable of that?

As mentioned in the first post of this thread- there are so many dependancies between the systems that setting somthing like that up (combined with hardware flakyness) makes that pretty much impossible.Grant
Darwin NT

A UPS is an emergency-use item, one that will sit unattended for long periods but when you want it, it has to work first time every time or it is worthless, and you wasted the money you spent. That's why it's a false economy to buy a cheap one.

Large installations perform regular disaster recovery tests to ensure, amongst may other things, that the UPS's are working as they should. Few home users do that. I wonder if the University has any policy on disaster recovery testing?

The principal cost is batteries. Battery technology is still waiting for its next breakthrough in terms of storage capacity, charge speed and reliability - we're still using wet cell technology which is more than 200 years old, only the chemicals have changed. Buying cheap batteries for a UPS is particularly pointless, as they will fail early and require replacement more frequently: you end up spending more, and with a less-reliable UPS.

Telephone exchanges used to have very large 48V batteries, massive numbers of wet cells, which powered the remote equipment directly. Not a UPS as such - there was no inverter to produce AC mains power from the battery.

I've read that telephone offices used to be required to have a UPS that could keep everything essential in that office running for three days. You might ask telephone offices if they have one they can donate. Warning - expect it to fill an entire room; I've seen one. It had a large rack of 2 volt cells, made with lead and something other than the usual acid.

I kinda think they might just be a bit too large!:-) Also they supplied 50V

<image deleted, no need to take up the extra space>

That is an accurate picture of a UK telephone exchange battery room as I used to work in telephone exchanges. I think that most nowadays have diesel generators

That is similar to what I remember from my school field trip to the nearby AT&T Long Lines facility in about 1983. They told us the batteries only needed to last for the 90 seconds or so it took for the diesel generator to start up.DavidSitting on my butt while others boldly go,
Waiting for a message from a small furry creature from Alpha Centauri.

That is an accurate picture of a UK telephone exchange battery room as I used to work in telephone exchanges. I think that most nowadays have diesel generators

A standard BT 50V battery room, which provided the ringing and telephony current. What was fun was seeing a spanner dropped across the overhead aluminium busbars and seeing it welded to them. Bernie is correct, all major Exchanges have standby diesel generators. No UPS will last for more than about 2 hours. The whole point of them is to allow the protected equipment to shut down safely without corruption of data.

That is an accurate picture of a UK telephone exchange battery room as I used to work in telephone exchanges. I think that most nowadays have diesel generators

A standard BT 50V battery room, which provided the ringing and telephony current. What was fun was seeing a spanner dropped across the overhead aluminium busbars and seeing it welded to them. Bernie is correct, all major Exchanges have standby diesel generators. No UPS will last for more than about 2 hours. The whole point of them is to allow the protected equipment to shut down safely without corruption of data.

Something about this reminds me of a UPS / Generator at an airfield. The UPS was good for 15 minutes. The generator had a 5 gallon tank - which was hooked up by a pump to the tank farm that the aircraft used...

During the first power outage that lasted more than 20 minutes, the power to the computers went off. The installer of the generator was called as it was not running. They arrived, and tested it. Nothing wrong they said.

During the second power outage that lasted more than 20 minutes the same thing happened.

During the third power outage that lasted more than 20 minutes and actually lasted more than 5 hours, the installers were able to get to the installation before the power turned back on. Remember that 5 gallon tank? It was empty. the pump that kept it full was connected to the mains side of the generator and was disconnected when the power was off.BOINC WIKI